Conventionally, cemented carbide comprised of crystal grains mainly formed of WC and binder phase mainly formed of iron group metal such as Co or Ni has been used for various cutting tools and wear resistant tools as it has superior hardness, toughness and modulus of rigidity. However, along with widened application of cemented carbide recently., there has been greater need for WC based cemented carbide having higher hardness and toughness.
In order to satisfy such demand, Japanese Patent Laying-Open Nos. 2-47239, 2-138434, 2-274827 and 5-339659 propose cemented carbide in which the WC crystal grains have a plate-like shape in order to realize hardness and toughness higher than the conventional cemented carbide.
Japanese Patent Laying-Open No. 5-339659 mentioned above discloses a cemented carbide in which more than 15% of WC crystal grains in the cemented carbide are plate-like WC crystal grains having maximum dimension of 110.about.10 .mu.m, which is twice or more of the minimum dimension. Japanese Patent Laying-Open No. 7-278719 or 8-199285 discloses an alloy containing plate-like WC crystal grains having the ratio of the maximum dimension with respect to the minimum dimension of 3.about.20 (hereinafter, this ratio will be referred to as aspect ratio: when a cemented carbide containing crystal grains mainly consisting of WC and a binder phase mainly consisting of an iron group metal contains plate-like WC crystal grains and an arbitrarily selected cross section of the cemented carbide is observed by a scanning electron microscope, the ratio of the maximum dimension with respect to the minimum dimension of an individual plate-like WC crystal grain at the arbitrary cross section).
In the proposals above, characteristics of the alloy can be improved to some extent. However, manufacturing cost has been increased, as special raw material powder or special method of manufacturing is employed. Further, the amount of generated plate-like WC crystal grains is unstable, resulting in unstable alloy characteristics.
Though toughness is improved to some extent by the generation of the plate-like WC crystal grains, strength of some plate-like WC crystal grains which coarsened too much is not necessarily higher as compared with WC crystal grains which are not coarsened, causing much variation in strength of the cemented carbide itself. Further, when WC crystal grains are coarsened, the alloy comes to have lower hardness. Therefore, development of WC based cemented carbide having more superior hardness and toughness has been desired.